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On her regular commute to the scientific station, biologist the researcher stoops near a small pond covered by thick plants and collects a small plastic audio recorder.

She had placed there through the night to record the distinctive calls of the Scinax quinquefasciatus, recognized by Galápagos researchers as an non-native threat with consequences that scientists are starting to comprehend.

Despite abounding with remarkable wildlife – such as ancient large turtles, marine lizards, and the well-known birds that sparked Charles Darwin's theory of evolution – the island chain near the coast of Ecuador had historically been devoid of amphibians.

In the late 1990s, this changed. Several small amphibians made their way from continental Ecuador to the archipelago, likely as stowaways on cargo ships.

Genetic studies suggest that, through time, there have been multiple accidental arrivals to the islands, and the frogs now have a firm presence on two islands: multiple locations.

The numbers is expanding so rapidly that researchers have been struggling to keep track, estimating numbers in the millions on each island, across urban and farming areas, but also in the protected natural reserve.

When the biologist marked amphibians and attempted to recapture them in the subsequent week and a half, she could locate only a single tagged frog occasionally, indicating their numbers were enormous.

They calculated 6,000 frogs in a single pond. "The calculations are still very conservative," states the researcher. "I am quite certain there are even more."

Deafening Noise and Rising Worries

The frogs' proliferation is clear from the acoustic disruption they create. "The amount of frogs and the noise – it's truly insane," comments the scientist.

For the researchers, their nocturnal vocalizations are helpful in determining their existence in far-flung areas, using recorders like the one near San José's office.

But local farmers say the calls are so loud they prevent sleep at night.

"During the wet season, I regularly hear their croaks and they're extremely loud," says a local coffee farmer from the island.

"At first it was a shock, seeing the initial frogs in the region," says Larrea Saltos, who started observing their large numbers about three years ago when one leaped on her palm as she was walking out of her front door.

Ecological Impact Stays Unknown

The sound isn't the fundamental problem, though. While the species has been in the islands for almost 30 years, experts still know very little about its effect on the islands' precariously balanced land and water environments.

On archipelagos, it is very typical for invasive species to prosper, as they have few of their enemies. The Galápagos counts 1,645 invasive species, many of which are significantly affecting the survival of its endemic ones.

A 2020 research suggests the non-native amphibians are voracious bug consumers, and might be unevenly consuming rare insects found exclusively on the archipelago, or reducing the food sources of the region's rare avian species, affecting the food chain.

Unusual Traits and Management Difficulties

The Galápagos amphibians have exhibited some unusual traits, including living in slightly salty water, which is uncommon for amphibians.

Their metamorphosis stage is also highly variable, with some larvae becoming frogs very rapidly and others taking a long time: the researcher observed one which remained as a larva in her laboratory for six months.

"We really don't know this aspect," she says, concerned the tadpoles could be affecting the region's freshwater, a very limited resource in the islands.

Techniques to curb the amphibians in the early 2000s were mostly ineffective. Conservation officers tried collecting large numbers by manual methods and slowly raising the salt content of ponds in without success.

Research suggests applying coffee – which is extremely toxic to amphibians – or using electrical methods could assist, but these methods aren't necessarily secure for other uncommon Galápagos organisms.

Lacking answers to more of the fundamental issues about their biology and impact, removing the amphibians might not even be the correct way to advance, says San José.

Financial Obstacles for Study

While she expects the increasing use of eDNA techniques and DNA examination will assist her team make sense of the invader, financial support for the research has been hard to obtain.

"Everybody wants to give funding for preserving frogs," says the researcher. "But it's more difficult to find funding for an invasive frog that you might want to control."